Formulation in Pharmacy Practice   2nd Edition

CARBAMAZEPINE
 
 
Carbamazepine is practically insoluble in water and soluble in alcohol.  It is a bitter substance with an unpleasant after-taste.  Suspensions are commercially available, and should be used whenever possible.  Carbamazepine has been reported to be stable for at least 30 days in a variety of formulations prepared from tablets.1,2 Tegretol® tablets (not controlled release) disperse easily and rapidly in water. Chewable tablets are also available.
Carbamazepine oral liquid is available in many countries and should be used whenever possible.

Formula 1

Carbamazepine 200mg per 5mL
 
Carbamazepine tablets 200mg 20   
Syrup to   100  mL
 
If the syrup is unpreserved add 0.1% parabens or, providing the pH is 5 or less, 0.1% sodium benzoate.
 
Expiry:  30 days
 
Storage:  Refrigerate.
Amber glass bottles and plastic oral syringes used in the study.1
Should be stored in airtight containers to prevent degradation.
 
Shake Before Use
 

 
NOTES
  1. The above formula is the simplest but the sugar content may be unacceptable.
    Alternative formulations utilising a base of (approximately) syrup 30mL, sorbitol 70% 8mL, glycerol 2mL, parabens 0.1%, water to 100mL1; or syrup 30mL, methylcellulose 1% 70mL, preserved with sodium benzoate2 have been proposed.
  2. Tegretol® tablets (not controlled release) disperse easily and rapidly in water.
    Chewable tablets are also available.
  3. The absorption characteristics and bioavaliability of the suspension may be different to that of the tablet.  In the study by Bloomer et al2 the extent of absorption was similar between tablet and suspension.  The suspension produced significantly earlier and higher peak concentrations.
  4. Carbamazepine suspension should be mixed with an equal volume of diluent (water or normal saline) before nasogastric administration to minimize adherence of the suspension to the tubing.3

REFERENCES
  1. Burkart G.J., Hammond R.W., Akers M.J.  Stability of extemporaneous suspensions of carbamazepine.
    Am J Hosp Pharm 1981; 38: 1929-31.
  2. Bloomer D., Dupuis L.L., MacGregor D., Soldin S.J.  Palatability and relative bioavailability of an extemporaneous carbamazepine oral suspension.  Clin Pharm 1987; 6: 646-49.
  3. Clark-Schmidt A.L.  Loss of carbamazepine suspension through nasogastric feeding tubes.
    Am J Hosp Pharm 1990; 47: 2034-37.

 
Formulation in Pharmacy Practice
2nd Edition